High-harmonic generation in metallic titanium nitride.

High-harmonic generation is a cornerstone of nonlinear optics. It has been demonstrated in dielectrics, semiconductors, semi-metals, plasmas, and gases, but, until now, not in metals. Here we report high harmonics of 800-nm-wavelength light irradiating metallic titanium nitride film. Titanium nitride is a refractory metal known for its high melting temperature and large laser damage threshold. We show that it can withstand few-cycle light pulses with peak intensities as high as 13 TW/cm2, enabling high-harmonics generation up to photon energies of 11 eV. We measure the emitted vacuum ultraviolet radiation as a function of the crystal orientation with respect to the laser polarization and show that it is consistent with the anisotropic conduction band structure of titanium nitride. The generation of high harmonics from metals opens a link between solid and plasma harmonics. In addition, titanium nitride is a promising material for refractory plasmonic devices and could enable compact vacuum ultraviolet frequency combs.

Negative Refraction in Time-Varying Strongly Coupled Plasmonic-Antenna-Epsilon-Near-Zero Systems.

Time-varying metasurfaces are emerging as a powerful instrument for the dynamical control of the electromagnetic properties of a propagating wave. Here we demonstrate an efficient time-varying metasurface based on plasmonic nano-antennas strongly coupled to an epsilon-near-zero (ENZ) deeply subwavelength film. The plasmonic resonance of the metal resonators strongly interacts with the optical ENZ modes, providing a Rabi level spitting of ∼30%. Optical pumping at frequency ω induces a nonlinear polarization oscillating at 2ω responsible for an efficient generation of a phase conjugate and a negative refracted beam with a conversion efficiency that is more than 4 orders of magnitude greater compared to the bare ENZ film. The introduction of a strongly coupled plasmonic system therefore provides a simple and effective route towards the implementation of ENZ physics at the nanoscale.

Synchrotron radiation from an accelerating light pulse.

Synchrotron radiation-namely, electromagnetic radiation produced by charges moving in a curved path-is regularly generated at large-scale facilities where giga-electron volt electrons move along kilometer-long circular paths. We use a metasurface to bend light and demonstrate synchrotron radiation produced by a subpicosecond pulse, which moves along a circular arc of radius 100 micrometers inside a nonlinear crystal. The emitted radiation, in the terahertz frequency range, results from the nonlinear polarization induced by the pulse. The generation of synchrotron radiation from a pulse revolving about a circular trajectory holds promise for the development of on-chip terahertz sources.

Patterned multilayer metamaterial for fast and efficient photon collection from dipolar emitters.

Solid-state quantum emitters are prime candidates for the realization of fast, on-demand single-photon sources. The improvement in photon emission rate and collection efficiency for point-like emitters can be achieved by using a near-field coupling to nanophotonic structures. Plasmonic metamaterials with hyperbolic dispersion have previously been demonstrated to significantly increase the fluorescence decay rates from dipolar emitters due to a large broadband density of plasmonic modes supported by such metamaterials. However, the emission coupled to the plasmonic modes must then be outcoupled into the far field before it succumbs to ohmic losses. We propose a nano-grooved hyperbolic metamaterial that improves the collection efficiency by several times compared to a conventional planar lamellar hyperbolic metamaterial. Our approach can be utilized to achieve broadband enhancement of emission for diverse types of quantum emitters.

Corrigendum: Controlling hybrid nonlinearities in transparent conducting oxides via two-colour excitation.

This corrects the article DOI: 10.1038/ncomms15829.

Controlling hybrid nonlinearities in transparent conducting oxides via two-colour excitation.

Nanophotonics and metamaterials have revolutionized the way we think about optical space (ɛ,µ), enabling us to engineer the refractive index almost at will, to confine light to the smallest of the volumes, and to manipulate optical signals with extremely small footprints and energy requirements. Significant efforts are now devoted to finding suitable materials and strategies for the dynamic control of the optical properties. Transparent conductive oxides exhibit large ultrafast nonlinearities under both interband and intraband excitations. Here we show that combining these two effects in aluminium-doped zinc oxide via a two-colour laser field discloses new material functionalities. Owing to the independence of the two nonlinearities, the ultrafast temporal dynamics of the material permittivity can be designed by acting on the amplitude and delay of the two fields. We demonstrate the potential applications of this novel degree of freedom by dynamically addressing the modulation bandwidth and optical spectral tuning of a probe optical pulse.

Enhanced Nonlinear Refractive Index in ε-Near-Zero Materials.

New propagation regimes for light arise from the ability to tune the dielectric permittivity to extremely low values. Here, we demonstrate a universal approach based on the low linear permittivity values attained in the ε-near-zero (ENZ) regime for enhancing the nonlinear refractive index, which enables remarkable light-induced changes of the material properties. Experiments performed on Al-doped ZnO (AZO) thin films show a sixfold increase of the Kerr nonlinear refractive index (n_{2}) at the ENZ wavelength, located in the 1300 nm region. This in turn leads to ultrafast light-induced refractive index changes of the order of unity, thus representing a new paradigm for nonlinear optics.

Experimental demonstration of titanium nitride plasmonic interconnects.

An insulator-metal-insulator plasmonic interconnect using TiN, a CMOS-compatible material, is proposed and investigated experimentally at the telecommunication wavelength of 1.55 µm. The TiN waveguide was shown to obtain propagation losses less than 0.8 dB/mm with a mode size of 9.8 µm on sapphire, which agree well with theoretical predictions. A theoretical analysis of a solid-state structure using Si(3)N(4) superstrates and ultra-thin metal strips shows that propagation losses less than 0.3 dB/mm with a mode size of 9 µm are attainable. This work illustrates the potential of TiN as a realistic plasmonic material for practical solid-state, integrated nano-optic and hybrid photonic devices.

Improving the radiative decay rate for dye molecules with hyperbolic metamaterials.

We directly demonstrate an improvement in the radiative decay rate of dye molecules near multilayer hyperbolic metamaterials (HMMs). Our comprehensive study shows a radiative decay rate for rhodamine 800 (Rh800) that is several times higher due to the use of HMM samples as compared to dielectric substrates. This is also the first experimental demonstration that multilayer hyperbolic metamaterials provide an increase in the radiative decay rate relative to those from either thin or thick gold films.

Demonstration of a spaser-based nanolaser.

One of the most rapidly growing areas of physics and nanotechnology focuses on plasmonic effects on the nanometre scale, with possible applications ranging from sensing and biomedicine to imaging and information technology. However, the full development of nanoplasmonics is hindered by the lack of devices that can generate coherent plasmonic fields. It has been proposed that in the same way as a laser generates stimulated emission of coherent photons, a 'spaser' could generate stimulated emission of surface plasmons (oscillations of free electrons in metallic nanostructures) in resonating metallic nanostructures adjacent to a gain medium. But attempts to realize a spaser face the challenge of absorption loss in metal, which is particularly strong at optical frequencies. The suggestion to compensate loss by optical gain in localized and propagating surface plasmons has been implemented recently and even allowed the amplification of propagating surface plasmons in open paths. Still, these experiments and the reported enhancement of the stimulated emission of dye molecules in the presence of metallic nanoparticles lack the feedback mechanism present in a spaser. Here we show that 44-nm-diameter nanoparticles with a gold core and dye-doped silica shell allow us to completely overcome the loss of localized surface plasmons by gain and realize a spaser. And in accord with the notion that only surface plasmon resonances are capable of squeezing optical frequency oscillations into a nanoscopic cavity to enable a true nanolaser, we show that outcoupling of surface plasmon oscillations to photonic modes at a wavelength of 531 nm makes our system the smallest nanolaser reported to date-and to our knowledge the first operating at visible wavelengths. We anticipate that now it has been realized experimentally, the spaser will advance our fundamental understanding of nanoplasmonics and the development of practical applications.

Effect of an optical negative index thin film on optical bistability.

We investigate nonlinear transmission in a layered structure consisting of a slab of positive index material with Kerr-type nonlinearity and a subwavelength layer of linear negative index material (NIM) sandwiched between semi-infinite linear dielectrics. We find that a thin layer of NIM leads to significant changes in the hysteresis width when the nonlinear slab is illuminated at an angle near that of total internal reflection. Unidirectional diodelike transmission with enhanced operational range is demonstrated. These results may be useful for NIMs characterization and for designing novel NIMs-based devices.

Coexistence of localized and delocalized surface plasmon modes in percolating metal films.

Near-field intensity statistics in semicontinuous silver films over a wide range of surface coverage are investigated using near-field scanning optical microscopy. The variance of intensity fluctuations and the high-order moments of intensity enhancement exhibit local minima at the percolation threshold. This reduction in local field fluctuations results from resonant excitation of delocalized surface plasmon modes. By probing the modification of the critical indices for high-order moments of intensity enhancement caused by the delocalized states, we provide the first experimental evidence for the coexistence of localized and delocalized surface plasmon modes in percolating metal films.

Enhancement of surface plasmons in an Ag aggregate by optical gain in a dielectric medium.

We have observed the compensation of loss in a metal by a gain in a dielectric medium in the mixture of an Ag aggregate and a Rhodamine 6G dye. The demonstrated sixfold enhancement of the Rayleigh scattering is the evidence of the enhancement of the surface-plasmon resonance. The reported experimental observation facilitates many applications of nanoplasmonics.

Near-field intensity correlations in semicontinuous metal-dielectric films.

Spatial intensity correlation functions are obtained from near-field scanning optical microscope measurements of semicontinuous metal-dielectric films. The concentration of metal particles on a dielectric surface is varied over a wide range to control the scattering strength. At low and high metal coverages where scattering is weak, the intensity correlation functions exhibit oscillations in the direction of incident light due to excitation of propagating surface waves. In the intermediate regime of metal concentration, the oscillatory behavior is replaced by a monotonic decay as a result of strong scattering and anomalous absorption. Significant differences in the near-field intensity correlations between metallic and dielectric random systems are demonstrated.

[Free radicals lipid peroxidation and level of R-proteins in non-specific aortoarteritis and hypertension]. / Svobodnoradikal'noe okislenie lipidov i uroven' R-belkov pri nespetsificheskom aortoarteriite i gipertonicheskoi bolezni.

Parameters characterizing free-radical oxidation of lipids (malonic dialdehyde, total serum antioxidative activity, ceruloplasmin, and superoxide dismutase) and the level of R proteins were studied in patients with nonspecific aortoarteritis and essential hypertension. Lipid peroxidation and the content of regulatory proteins were increased in the patients, the shifts being the most expressed in nonspecific aortoarteritis of the maximum activity.

Geometrical renormalization approach to calculating optical properties of fractal carbonaceous soot.

We develop a theoretical approach to calculating optical properties of carbonaceous soot in the long-wavelength limit. Our method is based on geometrical renormalization of clusters; it avoids both the inaccuracy of the dipole approximation in its pure form and the numerical complexity of rigorous direct methods of solving the EM boundary problem. The results are verified by comparison with the experimental measurements for specific extinction of diesel soot in the spectral region from 0.488 microm to 0.857 cm that were performed by Bruce et al. [Appl. Opt. 30, 1537 (1991)]. The theory leads to analytical expressions that are applicable to different soots, with various geometrical properties and optical constants. We show that the functional form of the long-wavelength asymptote of the specific extinction can depend critically on a parameter characterizing the sample geometry, and we identify the critical value of this parameter.

[Prevention of neuroleukemia by intrathecal administration of cytosar and methotrexate in acute lymphoblastic leukemia in adults]. / Profilaktika neiroleikemii intratekal'nymi vvedeniiami tsitozara i metotreksata pri ostrom limfoblastnom leikoze u vzroslykh.

AIM: To find out whether efficacy of neuroleukemia (NL) prevention by intrathecal administration of cytosar and methotrexate in remission induction phase in adult patients with acute lymphoblastic leukemia (ALL) depends on the risk factors. MATERIALS AND METHODS: The study covered 68 ALL patients. The diagnosis was made by cytological, histological and cytochemical tests of the peripheral blood and bone marrow. Immunophenotyping was performed in 48 patients. The treatment followed the German protocol 04.89 in modification of the Hematological Research Center of the Russian Academy of Medical Sciences. Prevention of NL consisted in intrathecal administration of cytosar (30 mg), methotrexate (15 mg) and dexamethasone (4 mg) once a week for 6 weeks beginning on induction day 1, further in consolidation, reinduction and once in 3 months in maintenance. Radiation of the brain was not conducted. Treatment of leuroleukemia consisted of intrathecal administration of the above drugs twice a week up to normalization of the liquor with subsequent their administration 5 times and craniospinal radiation in a dose 36 Gy. Further intrathecal administrations were made according to the protocol. RESULTS: Correlation was not found between age of the patients and frequency of neuroleukemia onset, between neuroleukemia incidence and peripheral blood leukocytosis at diagnosis. Results of NL prevention with cytosar and methotrexate given intrathecally in induction of remission (14.6% of neurorecurrences) are comparable with the results of NL prevention by radiation of the brain with intrathecal administration of methotrexate obtained in the German cooperative trial. CONCLUSION: NL prevention in ALL adult patients by intrathecal cytosar and methotrexate in remission induction is effective.

Near-field optical studies of local photomodification in nanostructured materials.

Fractal aggregates of silver nanoparticles are studied experimentally using atomic force microscopy and photon scanning tunnelling microscopy. Large changes in the near-field optical response of fractal aggregates are observed after the irradiation of samples with nanosecond laser pulses. The threshold energy density for photomodification using a 532 nm laser is measured to be 9 mJ cm(-2). It is shown that photomodification-induced changes in the local optical response can be two orders of magnitude larger than changes in far-field absorption.

Percolation-enhanced nonlinear scattering from metal-dielectric composites.

It is shown that large percolation-enhanced nonlinear scattering occurs in metal-dielectric random composites near the percolation threshold. The enhancement is due to giant local electric field fluctuations that are extremely inhomogeneous and consist of spatially separated sharp peaks, "hot" spots, where the local field is greater by many orders of magnitude than the applied field.

[Viral hepatitis B and C in patients with acute leukemias]. / Virusnye gepatity B i C u bol'nykh ostrymi leikozami.

Enzyme immunoassay has been used in 102 patients with acute leukemia (AL) and 340 donors to identify serological markers of hepatitis B virus (HBV) and hepatitis C virus (HCV): HB-sAg, anti-HBs, anti-HBc, anti-HBc IgM, HBeAg, anti-HBe. At the moment of AL diagnosis in 50 patients with acute myeloid leukemia and in 28 patients with acute lymphoblastic leukemia at least one HBV marker was found in 68% and 71%, respectively, HBsAg in 12% of patients with AML and 25% of those with ALL. In remission maintenance, HBsAg was registered in 83% of patients with AML and 44% of those with ALL. Anti-HCV in diagnosis of acute leukemia were detected in 1.28% of patients, 12 months after in 40% with ALL and 67% with AML. In examination of the donors at least one HBV marker was found in 36%, HBsAg in 2.1%, anti-HCV in 1.86% of the examinees. It is inferred that acute leukemia patients are often infected with HBV and in long-term follow-up demonstrate reactivation of viral infection, though infection with mutant B viruses is also possible. HCV is a main cause of posttransfusion hepatitis in this group of patients.